Why Eshell? - Part 1

From time to time, I got asked why I use eshell as my main terminal. There are multiple reasons I do so and covering all of them in one post would be too long. Instead, I would like to start with a high level bullet points and address each one in a separate blog post with working code examples where I can point my coworkers and friends to them so they can pick and choose as they wish.

1. Long running command notification and time
2. Cross session history
3. Interactive ido completion
4. Unified interface (shell prompt buffer as regular emacs buffer)
5. Plan9 Style Shell prompt (Think of it as bash REPL)
6. Multiple terminal management
7. Super charge bash with elisp
8. Eshell aliases that puts bash aliases to shame :)

Let us start with how you can accomplish the first item from the list above. Following 18 lines of elisp will give you the super power of:

• How long a command took to run as if you typed in time <command>
• Notify you that the long running command finished in x second even if you switch away from Emacs saving you the trouble of constantly checking back. As a bonus, you can set the notification threshold for long running commands that you want to run async.

;; eshell time and notification
(defvar-local eshell-current-command-start-time nil)

(defun eshell-current-command-start ()
  (setq eshell-current-command-start-time (current-time)))

(defun eshell-current-command-stop ()
  (when eshell-current-command-start-time
    (let ((elapsed-time (float-time
			 (time-subtract (current-time)
					eshell-current-command-start-time))))
      (if (> elapsed-time 30)
	  (tooltip-show (format "Finished in: %.0fs" elapsed-time))
	(eshell-interactive-print
	 (format "Time: %.0fs\n" elapsed-time))))
    (setq eshell-current-command-start-time nil)))

(defun eshell-current-command-time-track ()
  (add-hook 'eshell-pre-command-hook #'eshell-current-command-start nil t)
  (add-hook 'eshell-post-command-hook #'eshell-current-command-stop nil t))

;; This line below installs time tracking and notification
(add-hook 'eshell-mode-hook #'eshell-current-command-time-track)
;; Once you eval above snippet in emacs, fire up M-x eshell, and type:
sleep 40
;; You can switch away from emacs and will be notified that above
;; command took 40s to run
;; To uninstall
;; (remove-hook 'eshell-mode-hook #'eshell-current-command-time-track)

Try doing above with some bashrc voodoo or plug-in that you have no control over. I have been there and done that and it is one of many reasons why I use eshell now. I hope someone finds it useful to his or her command line work flow. Happy eshelling!